Can I have a list of where all the energy cells are?

Energy Cell 1: Valhalla
This is the simplest of Energy Cells you can find. From entering the Valhalla (yes you did spell it right the first time) approach the door and then head right. Something should be glowing under the wrecked crashed ship, which should be the first Energy Cell.

Energy Cell 2: Bryyo
This is located where you upgrade your ship for the first time. From facing the force field protecting a red door, head left I think to some air vents. Find the vents easier by being in scan mode, and it should say something about it being able since it's made out of something. Use your Morph Ball Form to get rid of the obstacle blocking it and go through the vent. It should be in where you end up, next to the vents.

Energy Cell 3: Norion- NEED Seeker Missles, Plasma Beam (Optional Items Needed- X-Ray Visor, Nova Beam)
From the first landing site (should be the northern most site), keep going until you find a Soldier next to a broken circuit board and a locked up door. Fix the circuit board with the Plasma Beam and the locked up door should be accessable. Go through it, and keep going until you reach a door with 5 switches that all of them needs to be hit at the same time. There is a small fight here, kill all the phazon enemies, then reach the door with the 5 switches. Use the Seeker Missle to open the door and head on through. Once you enter Generator B, a Metriod Hatcher should show up. I don't wanna tell you how to really fight it, but there is an alternative. Use the X-Ray Visor and the Nova Beam to kill it in 1 shot. Then a Tunnel will open up, use your Morphball to go through it and then Energy Cell #3 awaits you.

Energy Cell 4: Bryyo- NEED Ship Grapple, Boost Ball
This is the most complicated Energy Cell to get, and I don't wanna explain how to get to places, but here's the important parts. Go the landing site of where you got your first ship upgrade, and head through a red door. Keep going until you reach a Golem's head, and use the Ship's Command to carry the head. Then find a room with a ship missle upgrade trapped in a spiral cage of somekind and a golem in the background with no head. Make the ship land the Golem's head there, and watch a cutscene. Then head to a new room you can access and find a slot where you can use the Boost Ball to activate a half-bridge. Once that is out of the way, get out of there and head to Thorn Jungle Landing Site. This place is where you had to deactivate the anti-air guns, or something like that. If you remember the second time where you had to deactivate something, go to that place. There should be a room you haven't been to connected to that area. In the area is a generator. If you can't find it, use the Command Visor until you find an Up-Arrow for lifting an object. Lift the generator once you find it and head through the morphball tunnel until you get through the tunnel and another slot will be there. Use the Boost Ball to activate it, and cross the bridge to get out of there. Look familiar? Good. Now head to the Hidden Court (look on your map for this) and there should be a spot for the generator you picked up a while back. Land it, and then a cutscene will show you how to get to the station where it will reveal the 4th Energy Cell.

Energy Cell 5: Skytown- NEED Boost Ball
You need this to keep going in the story. This should be where you pass Phazon Metroids that are contained in some kind of containers. Keep going until you reach the Seeker Missles, and the Energy Cell is right next to it. Pick it up, and it goes dark, but gives you the Seeker Missles. Just be careful on your way out.

Energy Cell 6: Pirate Command
You need this to keep going in the story. It's specifically in the Command Courtyard. I forgot how to get there, but you should get it when you are hunting for the Acid Rain Suit upgrade. It should be where you are in a Morph Ball Puzzle of some kind.

Energy Cell 8: Ellysia-NEED Grapple Voltage
If you remember where you fought the Defense Drone is, then head there. If you can't find it, find an area where you need to give energy to a Morph Ball Elevator to activate it. It's more specifically in the Ballista Storage area. You need to overload 2 fans, and the Energy Cell will show itself.

I really did forget how to get to the other 2 Energy Cells are, but I remember their locations.

Energy Cell 7: Metroid Processing in the Pirate Homeworld-NEED Plasma Beam, X-ray Visor
Energy Cell 9: Phazon Quarry in the Pirate Homeworld-NEED Nova Beam, X-ray Visor

You need all 9 Energy Cells in order to go through all of Vahalla.